1. Field of the Invention
This invention relates to a tipped surgical suture and a method and apparatus for making same and a combined tipped suture and surgical needle. In particular, it relates to a cyanoacrylate tipping agent for braided sutures to prevent brooming and to increase stiffness, thereby facilitating attachment of the suture to a surgical needle.
2. Background of the Art
For many years, surgeons have employed needle-suture combinations in which a suture or ligature is attached to the shank end of a needle. Such needle-suture combinations are provided for a wide variety of monofilament and braided suture materials, both absorbable and non-absorbable, e.g., catgut, silk, nylon, polyester, polypropylene, linen, cotton, and absorbable synthetic materials such as polymers and copolymers of glycolic and lactic acid.
Needle-suture combinations fall into two general classes: standard, or non-detachable, needle attachment and removable, or detachable, needle attachment. In the case of standard needle attachment, the suture is securely attached to the needle and is not intended to be separable therefrom, except by cutting or severing the suture. Removable needle attachment, by contrast, is such that the needle is separable from the suture in response to a force exerted by the surgeon. Minimum acceptable forces required to separate a needle from a suture (for various suture sizes) are set forth in the United States Pharmacopoeia (USP). As to detachable needles, the United States Pharmacopoeia prescribes minimum individual pull-out forces and minimum average pull-out forces as measured for five needle-suture combinations. The minimum pull-out forces for both standard and removable needle-suture attachment set forth in the United States Pharmacopoeia are hereby incorporated by reference.
One typical method for securing a suture to a needle involves providing a cylindrical recess in the shank end of a needle and securing a suture therein. For example, U.S. Pat. No. 1,558,037 teaches the addition of a cement material to such a substantially cylindrical recess to secure the suture therein. Additional methods for bonding a suture within a needle bore are described in U.S. Pat. Nos. 2,928,395 (adhesives) and 3,394,704 (bonding agents). Alternatively, a suture may be secured within an axial bore in a needle by swaging the needle in the region of the recess. See, e.g., U.S. Pat. No. 1,250,114. Additional prior art methods for securing a suture within a needle bore include expansion of a catgut suture through the application of heat (U.S. Pat. No. 1,665,216), inclusion of protruding teeth within the axial bore to grasp an inserted suture (U.S. Pat. No. 1,678,361) and knotting the end of the suture to be inserted within the bore to secure the suture therein (U.S. Pat. No. 1,757,129).
Methods for detachably securing a suture to a needle are also well known. For example, U.S. Pat. Nos. 3,890,975 and 3,980,177 teach swaging a suture within a needle bore such that the suture has a pull-out value of 3 to 26 ounces. Alternative detachable attachment methods include providing a weakened suture segment (U.S. Pat. No. 3,949,756), lubricant tipping the end of a suture to be inserted in the axial bore of a needle (U.S. Pat. No. 3,963,031) and pre-tensioning a suture that is swaged within an axial needle bore (U.S. Pat. No. 3,875,946). See also, U.S. Pat. Nos. 3,799,169; 3,880,167; 3,924,630; 3,926,194; 3,943,933; 3,981,307; 4,124,027; and, 4,127,133.
Another method for attaching a suture to a needle involves the use of tubing which is secured to the shank end of the needle and to the suture. For example, U.S. Pat. No. 1,613,206 describes the use of a tubing (preferably silver) which is secured to the shank end of a needle and to a ligature. It is suggested that the tube may be attached to the needle by pressure or soldering and to the ligature by pressure or cementing. It is also suggested that the shank of the needle be of reduced cross section and that the furthest extremity of the reduced diameter shank section be provided with a spike or point upon which the suture may be secured prior to tube application.
U.S. Pat. No. 2,240,330 describes a tubing attachment method whereby the tubing and suture are releasably secured to the needle. In particular, the needle and tubing are provided with cooperating catch and abutment means which are released one form the other by rotating the needle 90.degree. relative to the tubing (or vice versa). The tubing is manufactured from spring-tempered carbon steel or chrome nickel steel and is secured to the suture by heating the tubing and then swaging to the suture.
U.S. Pat. No. 3,311,100 related to a flexible composite suture having a tandem linkage. The needle is secured to a flexible suture leader manufactured from a readily sterilizable plastic such as nylon, linear polyethylene, isostatic polypropylene, polyester, silk or other proteinaceous material, e.g., by inserting and crimping the leader within an axial bore in the needle shank. The opposite end of the suture leader is crimped within a connector sleeve of a thin walled metal tubing, e.g., stainless steel. The opposite end of the tubing is crimped around a steel suture, e.g., monofilament stainless steel.
U.S. Pat. No. 3,918,455 describes a needle-suture attachment wherein a hollow suture portion is secured to the shank end of a needle which is of reduced cross-section as compared to the remainder of the needle.
Additional patents which describe the use of tubing to effect suture-needle attachment include U.S. Pat. Nos. 4,672,734 (forming needle from U-shaped metal plate around suture), 4,359,053 (silicone tubing), 3,835,912 (laser welding of metal tube to needle), 2,814,296, 2,802,468 (chamfered tubing ends), 2,302,986, 2,240,330, 1,981,651 (needle and tubing screw threaded), 1,960,117, and 1,591,021.
In addition to the needle-suture constructions of the aforedescribed pull-out variety, it is known from U.S. Pat. No. 4,805,292 to provide a needle-suture combination in which a suture cutting edge is formed at the shank end of the needle. However, the combined needle-suture device of U.S. Pat. No. 4,805,292, like others described above, possesses a suture tip-receiving axial bore, or recess, formed in the butt end of the needle and as such is subject to the disadvantages recounted above which are associated with a needle possessing an axial bore.
Insertion of sutures into a hole, recess or tube for attachment to surgical needles presents problems peculiar to suture needle combinations. Braided multifilament sutures in particular are difficult to insert into the very small aperture of a surgical needle: unless modified, they are too limp for the suture tip to be controlled for insertion and they have a tendency to "broom", i.e., the filaments have a tendency to flare out at the cut end so that the diameter of the cut end exceeds the diameter of the needle hole. Various techniques have been employed to modify sutures to overcome the problems of limpness and brooming. One known method employs a tipping agent, which is a material used to coat the suture to stiffen the filaments and adhere them together.
Typically, a suture to be tipped is first placed under tension to reduce slack so that the suture may be maintained in a predetermined position on a frame or rack or other suture holding device. Optionally, the tension may be such as to reduce the diameter of the suture. See Canadian Pat. No. 1,009,532. The suture is then dipped into the tipping solution and allowed to dry while under tension. The sutures are then dried, such as by being warmed in a drying oven at about 225.degree. F. for about 10 minutes. After drying the sutures can be cut and released from tension. The process results in a tipped end on each side of a cut. Where tension has optionally been employed to reduce the suture diameter, release of said tension will allow the suture to expand to its original diameter except at the tipped end portion. This can facilitate insertion of the end into a needle.
Tipping agents may be dissolved in solvents to form dipping solutions. By way of example, Mariotte mixture is a dipping solution comprising nylon dissolved in isopropyl alcohol. Other polymers and solvents may also be used. Gould mixture is a dipping solution comprising nylon dissolved in methanol. At least one major manufacturer of surgical needles recommends use of Mariotte mixture or Gould mixture for tipping sutures. A multitude of other tipping agents, including polymers and solvents, have been proposed. For example McGregor U.S. Pat. No. 3,890,975 discloses coating the suture with a binding resin or adhesive. The composition may be any non-toxic adhesive composition, either organic, inorganic or a hybrid. Suitable organic materials are such natural products as starch, dextrin, asphalt, animal and vegetable proteins, natural rubber, shellac, semi-synthetic products such as cellulose nitrate and the other cellulosics, polyamides derived from dimer acids, castor-oil based polyurethanes; such well-known synthetic resins as vinyl-type addition polymers, both resins and elastomers; polyvinyl acetate, polyvinyl alcohol, acrylics, unsaturated polyesters, butadiene/acrylonitrile, butadiene/styrene, neoprene, butyl rubber, polyisobutylene; and polymers formed by condensation and other step-wise mechanisms, i.e., epoxies, polyurethanes, polysulfide rubbers, and the reaction products of formaldehyde with phenol, resorcinol, urea, and melamine. McGregor states that particularly preferred bonding compositions are epoxide resins and polyester resins.
Schmitt U.S. Pat. No. 3,736,646 discloses that it is known to tip braided sutures by dipping the end of the suture in a plastic such as a solution in isopropyl alcohol. Schmitt suggests that for absorbable sutures an absorbable tipping agent is desirable, and proposes that a copolymer of lactic and glycolic acid dissolved in a suitable organic solvent, such as xylene or toluene, be applied to tip the suture.
Nichols U.S. Pat. No. 2,734,506 discloses a dipping solution of polymers of methacrylic acid esters in an organic solvent such as toluene, xylene acetone, ethyl acetate, methylethyl ketone, or naphtha.
Shepherd et al. U.S. Pat. No. 3,849,185 discloses the use of an acrylic casting syrup as a tipping agent, the syrup being fully polymerized after being applied to the suture.
In addition, paraffin/hexane solution (10% paraffin) has been used as a suture coating agent as well as Arrochem (.TM.), a nylon resin plus methanol composition manufactured by ArroChem, Inc. of 201 Westland Farm Road, Mt. Holly, N.C. 28120, and SILASTIC (.TM.) Medical Adhesive (a silicon elastomer composition manufactured by Dow Corning Co.
Although dipped sutures prepared in accordance with the above procedures may have been used successfully, there are several drawbacks with the use of tipping solutions. The main problems relate to tipping consistency and process control. Non-uniform solvent evaporation, which may be caused by variations in the solvent, oven temperature and heating time can result in inconsistent tipping. Furthermore, the dried residue of polymer left after evaporation can flake off or develop cracks.
Another method which has been employed for treating sutures involves melt fusion, as described in U.S. Pat. No. 4,832,025, issued to Coates. The suture is heated to a temperature at least high enough to "melt fuse" a portion of the outer filaments of the suture. According to Coates, such temperature is typically about 260.degree. C. to 300.degree. C. (500.degree. F. to 572.degree. F.). Exposure of synthetic sutures to such extreme temperatures melt fuses the filaments, and the melt fused suture portion stiffens upon cooling. Melting of the filaments has the effect of holding the filaments together when the suture is cut. It also causes stiffening of the suture which facilitates insertion of the suture end into the drilled hole of a needle. However, the melt fusion of suture has significant drawbacks.
Firstly, the melt fusion of filaments weakens the suture, whose tensile strength is degraded in proportion to the extent of melt fusion.
Secondly, melt fusion causes an irreversible change in the filaments which result in permanent stiffening and permanent loss of tensile strength.
Thirdly, with the extreme temperatures disclosed by Coates for melt fusion an inconveniently short heating cycle is required. For example, for a size 3/0 silicone coated polyester suture heated to between 260.degree. C. to 300.degree. C. in a 4 mm. diameter heating tunnel, the heating time is no more than about 3 seconds. Such short heating times make it difficult to control the process and leads to inconsistencies and variations in the melt fused tipping process
A further consideration pertinent to suture tipping is that sutures are often prepared with lubricant coatings such as silicone or fatty acid salts in order to increase lubricity and to improve "tie-down" performance, i.e , the ease of sliding a knot down the suture into place. Such lubricant coatings typically are incompatible with the materials and methods currently employed for tipping sutures. In particular, prior known tipping agents do not adhere well to lubricant coated sutures, which may result in inconsistent tipping or an undesirable reduction of suture-needle pull out force. The melt fusing method of tipping may destroy the lubricant coating or render it less effective in areas away from the needle.
A method of and apparatus for tipping surgical sutures has been discovered which may be used to tip both uncoated and coated sutures and which provides superior stiffening of the suture for insertion into an opening to attach the suture to a needle.